1. Field of the Invention
This invention relates to thermal adhesive vibration damping sheets, and more particularly, to thermal adhesive vibration damping sheets which are resistant against blocking during storage in stacked form and well adhere to sheet steel by heat fusion.
2. Description of the Related Art
In the past, sheets were often laid on sheet steel and similar members for damping the vibration thereof. Most vibration damping sheets were formed of thermal adhesive material and prone to blocking with each other when they were stored in a stacked form, especially at high temperatures as encountered in summer, because of softening at such temperatures or bleeding of oil from the sheets. One prior art approach for preventing blocking was by dispersing non-adhesive powder such as talc to the surface of vibration damping sheets prior to stacking and shelf storage. This approach, however, had several problems including the scattering of talc or other non-adhesive powder which would aggravate the working environment, and deficient adhesion of vibration damping sheets to sheet steel. Moreover, the prior art vibration damping sheets had poor low-temperature impact resistance so that if sheet steel covered with a vibration damping sheet is impacted at low temperatures as encountered in winter, the vibration damping sheet could separate from the underlying sheet steel.
It was proposed to solve these problems by covering vibration damping sheets on their surface with film for preventing scattering of talc and other non-adhesive powder (Japanese Patent Application Laid Open Nos. 115249/1981 and 115665/1981) and by coating an emulsion to the surface of vibration damping sheets (Japanese Patent Application Laid Open No. 252476/1987). The former technique could preventing non-adhesive powder from scattering, but failed to overcome deficient adhesion of vibration damping sheets to sheet steel. The coating emulsion used in the latter technique was insufficient to prevent vibration damping sheets from blocking.
Therefore, an object of the present invention is to provide a thermal adhesive vibration damping sheet which is resistant against blocking during shelf storage of a sheet stack, well adhesive to sheet steel by heat fusion, resistant against peeling from the underlying sheet steel at low temperatures, and efficient to manufacture.